Avian influenza is a common disease in birds. Subtype H5N1 AIV has caused an outbreak of avian influenza that is spreading incessantly to many regions of the world (14). The affected areas include Europe, the Middle East and particularly Asia. According to the World Health Organization (“WHO”), as of April 2006, about one hundred human deaths had occurred as a result of H5N1 avian influenza, and the situation seems to be deteriorating. See WHO website (11). While AIV infection in humans is rare, there have been times in the past in which the occurrence of new AIV subtypes that are able to cross species barriers have caused deadly influenza pandemics (2, 8, 10).
Influenza viruses are classified according to their nucleoprotein and matrix protein antigenic specificity. These viruses are categorized mainly into A, B and C serotypes, with type A having eight RNA segments that encode ten viral proteins. All known type A influenza viruses originated in birds. This category of virus can infect other species, such as horses, pigs, owls and seals, and poses a threat to humans as well (22). Influenza A virus is further divided into subtypes according to the antigenic nature of the envelope glycoproteins, hemagglutinins (“HAs”), H1 through H16, and neuraminidases (“NAs”), N1 through N9 (10, 12, 19). It is believed that proteolytic cleavage of HA protein at the HA1-HA2 junction is related to the pathogenicity in avian strain and that the presence of hydrophobic amino acids around this cleavage site are characteristic of the H5 subtype. In addition, the HA protein is believed to mediate attachment to host cell sialoside receptors and subsequent entry by membrane fusion (17), and HA protein is thought to serve as a primary target for neutralizing antibodies (19).
This invention relates to monoclonal antibodies and related binding proteins that bind specifically to AIV. Monoclonal antibodies (“mAbs”) are a substantially homogeneous population of antibodies derived from a single antibody-producing cell. Thus all antibodies in the population are identical and of the same specificity for a given epitope (5). The specificity of the mAb responses provides a basis for an effective diagnostic reagent. Monoclonal antibodies and binding proteins derived therefrom also have found utility as therapeutic agents.
Because of the risk that AIV infection poses to wildlife, domesticated animals and humans, there is a pressing need for a fast, specific and reliable method for detecting the virus in tissue specimens. In particular, the ability to detect the virus in preserved specimens, such as formalin fixed specimens embedded in paraffin and in frozen sections, is important to the ability to diagnose the disease and monitor its progress. To date, there have been no reports of effective methods for diagnosis of the highly pathogenic H5N1 AIV strains using H5 subtype monoclonal antibodies. Accordingly, the present invention represents a breakthrough in the diagnosis and surveillance of H5N1 and other H5 strains.